90GHz designs have been demonstrated on 8HP, so best guess would be 8HP. It's not like they have any specs that would drive them to require a process more advanced than the minimum fT/fMax needed to function.

Les makes an excellent point; a relatively low power radar that can see "kilometers" ahead sounds like a robust solution for highway travel. In an aircraft, it would take quick action to avoid revealed obstacles.

I remember when phased array radar was billboard sized, consumed multi-MW and something you put on a ship or located in the Frozen North to watch for nasties coming over the pole. And it still does that...
It's a little scary to think of what can be done with this technology on a small scale - the surveillance potential is incredible. Should we be glad or worried - or both?

Remember, just because you're paranoid, doesn't mean they're NOT watching you.
When I wrote the above I was very aware of not only the potential for abuse, but that potential would be consciously and carefully built in.
But this is nothing new. LTE, and God knows what else, has a 'Legal Intercept' hook built in. Not only can your communications be tapped but your phone or tablet can be commanded to turn on camera and / or microphone.
Intrusive government is a very big problem. It's not a technical problem though.